Various electrochemical devices utilizing solid polymer electrolytes (herein abbreviated SPE) are known. As apparatuses for generating electrical energy, U.S. Pat. Nos. 3,134,697, 3,297,482 and 3,432,355 for example, disclose fuel cells.
It is also known that the SPE's can be used in electrolysis cells for performing an electrolytic reaction by supplying electric energy, apparatuses for generating gases such as hydrogen or oxygen or gas concentrating apparatuses for electrolyzing water, etc. (see, for example, U.S. Pat. Nos. 3,489,670 and 4,039,409).
Attempts have been made recently to use SPE's in various other industrial electrolysis apparatuses. For example, Japanese Patent Application (OPI) No. 52297/78 discloses an electrolysis apparatus for producing sodium hydroxide and sulfuric acid by electrolyzing an aqueous solution of sodium sulfate.
Application of SPE's to electrolyzing an aqueous solution of hydrochloric acid is described in Japanese Patent Application (OPI) Nos. 95996/79 and 97581/79.
Suggestions have also been made to apply SPE's to the production of chlorine and sodium hydroxide by electrolysis of an aqueous solution of sodium chloride which now occupies an important position in the electrolysis industry. Such a technique has already been disclosed, for example, in Japanese Patent Application (OPI) Nos. 102278/78, 93690/79, 107493/79, and 112398/79.
These SPE electrolysis apparatuses comprise an ion exchange resin membrane as an electrolyte diaphragm and an anode catalyst material and a cathode catalyst material in a layer bonded directly to the both surfaces of the membrane. Such an apparatus can be employed to electrolyze an aqueous solution by passing an electric current from a current supplier in contact with the electrode catalyst layer, and is characterized by the distance between the electrodes being minimized to the thickness of the membrane, and theoretically, no electrolyte solution exists between the electrodes. Accordingly, the size of the apparatus is drastically reduced and electric resistance arising due to the presence of electrolyte solution and bubbles generated between the electrodes, which cannot be avoided in usual electrolysis apparatuses, is minimal and can be ignored. Correspondingly, the electrolysis voltage can be decreased as compared with that required for the conventional diaphragm method, ion exchange membrane method, etc., and this is why the SPE method provides an excellent energy-saving electrolyzing system.
Since in conventional SPE electrolyzing apparatuses, an electrode catalytic substance layer such as carbon, metals, or metal oxides is integrally held to the surface of an organic ion-exchange resin membrane, and an electric current supply means is brought into contact with the catalytic material layer, various difficulties in performance, manufacture and operation are encountered as described below.
(a) It is quite difficult to bond the electrode catalytic material layer firmly in a uniform thickness to the entire surface of the membrane, and also to control the area of the bonded portion freely.
(b) Bonding of the electrode catalytic material layer requires a binder, and this correspondingly increases the electric resistance of the membrane.
(c) Since an ion exchange resin membrane is mechanically weak and is readily destroyed at high temperatures, various restrictions in manufacture, such as the inapplicability of the usual thermal decomposing method, sintering method, spraying method, etc., exist. Thus, it is difficult to bond firmly the electrode catalyst layer having superior activity.
(d) There is a difference in life between the ion exchange resin membrane and the electrode catalytic material. Hence, in a unitary structure composed of these materials, it is impossible in practice to exchange, repair, or recover them separately during or after use in electrolysis.
(e) Since a current supplier is to be contacted with the very thin electrode catalyst layer, the ion exchange resin membrane and the electrode catalyst layer are susceptible to damage. To obtain sufficient current density and uniform current distribution, current must be supplied at many positions. Thus, the structure of the current supplier becomes complex, and contact resistance tends to increase due to poor contact, corrosion, etc. of electrical contacts.